As a material for packing a case in which a magnetic recording medium such as a magnetic disc, an optical recording medium such as an optical disc and further a recording medium such as a magneto-optical disc is accommodated, there has been hitherto employed a heat shrinkable film such as a biaxial stretching polypropylene film or a biaxial stretching polyvinyl chloride film. The heat shrinkable film of this type is used to pack the case in which the above-described recording medium is housed, then superpose respective end parts and perform a heat sealing process in the superposed parts so that the case is packed. Further, the entire part of heat shrinkable film which packs the case is heated to heat-shrink the film by several % so that the heat shrinkable film tightly sticks to the outer peripheral surface of the packed case to seal the case.
Now, a procedure for packing the case in which the recording medium is accommodated by using the heat shrinkable film as the packing material will be specifically described below.
In order to pack a case 112 as an object to be packed by using a film type packing material 101, the case 112 is initially mounted on one end side of the spread packing material 101, as shown in FIG. 1A. Then, as shown in FIG. 1B, the case 112 is wrapped by the packing material 101. At this time, the back surface side of an end part 102 in one side of the packing material 101 is superposed on the surface of an end part 103 in the other side. Here, the back surface side means an inside surface opposed to the case 112 side to be packed. The surface side means a surface facing an external part opposite to the case 112 when the case 112 is packed.
Then, a part between the one end part 102 and the other end part 103 of the packing material 101 which are superposed one upon another is heated to perform a heat sealing process (See FIG. 1B). At this time, the packing material 101 is formed in a tubular shape to wrap the case 112 as shown in FIG. 1B.
Subsequently, both the end parts 102 and 103 are superposed together and subjected to the heat sealing process to obtain the packing material 101 in a tubular form. Thus, narrow parts 104 and 105 of the packing material 101 which respectively protrude from both the end faces of the case 112 and correspond to the narrow parts of the case 112 are folded on the end faces of the case 112 as shown in FIG. 1C. Then, the wide parts 106 and 107 of the packing material 101 which respectively protrude from both the end faces of the case 112 and correspond to the wide flat surfaces of the case 112 are folded onto the narrow parts 104 and 105 folded on the end faces of the case 112 and superposed thereon, as shown in FIG. 1D. Then, parts provided in the narrow parts 104 and 105 of and the wide parts 106 and 107 of the packing material 101 superposed respectively on the end faces of the case 112 are heated to perform a heat sealing process as shown in FIG. 1E.
As the heat shrinkable film forming the conventionally employed packing material, there have been used films made of polypropylene, polyvinyl chloride or the like as materials. When the packing material using these materials are thrown away and discarded after it is opened, the packing material may possibly cause an environmental contamination.
Thus, it is studied to compose the packing material of a biodegradable film in place of the above-described materials. However, a stretched biodegradable film does not generally have heat sealing characteristics. Accordingly, in the packing material using the biodegradable film, after an object to be packed is packed by the packing material, superposed parts cannot be heated to perform a heat sealing work. Therefore, when the biodegradable film is used, a packing method similar to that of a case in which the packing material having the above-described heat sealing characteristics cannot be utilized.
In order to make it possible to use the packing material made of the biodegradable film like the conventionally used packing material, may be considered such a method as to previously apply a heat sealing agent to the biodegradable film to form a sealing agent layer and to carry out a heat sealing process by using the heat sealing agent layer.
In the above-described packing manner as shown in FIG. 1, that is, in such a manner as to pack an object to be packed by a packing material by a caramel wrapping method, the front surface and the back surface, the front surfaces and the front surfaces, and the back surfaces and the back surfaces need to be respectively heat-sealed together on the end faces of the case on which the end parts of the packing material are folded from a state in which the packing material is folded.
For realizing such a heat sealing process, it may be suggested that the heat sealing agent layers are formed on the entire surfaces of both the front and back surfaces of the packing material. However, when the heat sealing agent layers are formed on the entire surfaces of both the front and back surfaces of the biodegradable film, the biodegradation characteristics of the biodegradable film will be deteriorated and a sufficient biodegradation capability cannot be exhibited.
Further, in case that the heat sealing agent layers are formed on the entire surfaces of both the surfaces of the packing material and the object to be packed is packaged by this packing material, the heat sealing agent layer will be exposed on the front surface of the packaged object. Thus, there inconveniently arises a problem that the packages are stuck to mutually when they are heated in the course of circulation of products.